Purification of naphthenic acids



Patented Oct. 18,1938 2,133,766

-UNITED STATES PATENT orr cs Frederick J. Ewing, Pasadena, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Original application March 12,

1934, Serial No. 715,181. Divided and this application February 28, 1936, Serial No. 66,221

11 Claims. (Cl. 260-514 This invention relates to naphthenic acids and tion of stills. The naphthenic acids which are more particularly refers to a process for their recovered as an overhead product of such a disdeodorization and decoloration, and is a divitillation are of a substantially improved color, sion of my copending application Serial No. but this color on standing rapidly darkens and .5; 715,181, filed March 12, 1934. in some instances becomes nearly as dark as be- It is an object of my invention to present a fore distillation. simple, eflicient and thoroughly satisfactory proc- A more efiicient and satisfactory method for ess for obtaining naphthenic acids of a light color removing this carbonaceous material consists in and bland odor. treating the crude or semi-refined naphthenic Naphthenic acids, such as may be obtained acids with any of the common oxygen contain- 10 by acidifying various alkaline liquors arising during inorganic acids, such as sulphuric acid of ing the refining of petroleum or shale oil fracsuitable concentration, whereby a coagulation tions, constitute a complex mixture of acidic comand separation of this carbonaceous material is pounds containing principally carbon, hydrogen brought about. The product obtained by this and oxygen. They range from comparatively low method of treatment which will be described in 15 boiling liquids to materials which are solid or greater detail later on, is of asomewhat improved semi-solid at ordinary temperatures. Their viscolor but still is inapplicable. without further cosities as well as their boiling points are gentreatment in any instances wherea light colored erally closely correlated to the viscosities and boilproduct is desired- 2Q ing points of the hydrocarbon fractions in which I have discovered that naphthenic acids from they are present. which the carbonaceous materials have been re- The crude naphthenic acids which are obtained moved by either of the two above identified procby acidifying the alkaline liquors referred to esses or. by any other physical ChBmiCal means above, contain varying amounts of phenols and such as those hereinafter set forth, may be carbonaceous materials and they possess a very WOrked p into a product 0f eXcellent light 0010! 25 dark to black color andadisagreeable odor. When which does not change or darken xpo re. these crude acids are freed from phenolic mateandbla m", by e t them subsequently rials by careful acidification, neutralization and to the removal of the carbonaceous materials with distillation as hereinafter described to produce an ad o material, such as y, fullers what will hereinafter be called semi-refined earth, Filtrol or activated carbo y 0 oper- 30 acids, the amount of carbonaceous materials apating, a distillation of the ap en c acids to pears to increase as a result of hi h 3% t 5% bring about a further improvement in color and thereof and sometimes even greater amounts Odor y be Eliminated s t eatment Withhave been encountered in the dephenolized naphadsorbent materials is substantially ineffective thenic acids. The major portion of this carwhere the carbonaceous materials have not been 5 bonaceous material i present in a, finely previouslyremoved. However, the acidtreatpended or colloidal state and is in most instances men? of the naphthehic acids for p p ses of not removable by settling or centrifuging. The removing the carbonaceous materials renders presence of this material is partially responsible them especially suitable for further p fic t n 49 for the dark and turbid color of the naphthenic y means f the adsorbent 0 acids and renders their sale as a commercial While it is customary to remove theresidual product practically impossible. It is, therefore, inorganic a d ty from the ap n c acids desirable to obtain naphthenic acids which are which have been treated with an oxygen-containsubstantially free from these undesirable mateins inorgan c ac d c as sulphuric a d for the is rials. removal-of the admixed carbonaceous materials,

It has been customary to distill the naphthenic BXperiments v d ca ed that the treatment acids to remove this carbonaceous material. with the adsorbent material may be substantially However, this distillation is not applicable in all improved by eliminating the water wash for the instances in that it is usually accompanied by removal of this inorganic acidity, and contacting 5.0. plugging of the still due to the presence of the the naphthenic acids with the adsorbent mate- 50 aforementioned carbonaceous material. Morerial in the presence of small amounts of an inorover, the equipment used for this distillation is ganic acid thus remaining in the naphthenic subject to a rapid deterioration due to the coracids. As a slight modification of" the above rosive action of the naphthenic acids on iron or method of treatment, I may activate the clay or on other metals normally used in the construcother adsorbent with small amounts of sulphuric 55- acid or any of the other acids set forth herein by adding these acids to the adsorbent and treating the naphthenic acids with the mixture of adsorbent and acid. Activation of the clay with acid salts, i. e. a salt which on solution liberates hydrogen ion, produces substantially identical results as in the case where an inorganic acid is used for activating the adsorbent. If desired, I may also add my inorganic acid directly to the naphthenic acids before adding the adsorbent material, whereby the same effect of activation of the adsorbent is obtained.

Therefore, my invention broadly resides in a process for obtaining naphthenic acids of a stable light color and bland odor which comprises removing the carbonaceous material present in these acids and subsequently treating the product so obtained by means of an adsorbing agent.

My invention likewise extends to a process for purifying and decolorizing naphthenic acids wherein the adsorbing agent used has been activated or treated with an inorganic acid such as sulphuric acid or with an acid salt such as sodium acid sulphate or sodium acid phosphate or the like.

The term alkaline liquor referred to earlier in this specification relates not only to the alkaline solution containing naphthenic acids and other materials taken up by the alkali on treating a petroleum fraction but also relates to the alkaline solution obtained by treating the extract phase which is formed on treating a petroleum fraction with a selective solvent such as liquid sulphur dioxide, dichlorethyl ether, nitrobenzene, furfural, isopropyl alcohol, dimethyl sulphate, etc., with caustic soda, caustic potash or any other alkaline reagent.

When an alkaline liquor, arising on treatment of petroleum fractions such as any of those described above, is acidified with any of the well known inorganic acids a distinct phase separates out which phase is then adjusted by means of sodium carbonate or sodium hydroxide (or their equivalents) to a pH of about 9. By so operating there is formed a mixture consisting of sodium naphthenates, phenols and admixed hydrocarbons which is then subjected to distillation which removes the phenols and hydrocarbons overhead. The still bottoms then consist of sodium naphthenates, which, when dissolved in water form a solution from which the semi-refined acids are, obtained by the addition of a mineral acid such as sulphuric acid.

These semi-refined naphthenic acids contain from 3% to 5% of carbonaceous material, only a small fraction of which is removable by settling or centrifuging. Apparently this material is present in some kind of colloidal suspension which renders its separation extremely difficult. In addition, they are of a red to dark black color rendering their use as a commercial product practically impossible.

In a copending application, Serial 'No. 696,914, there is set forth a process for removing carbonaceous materials from crude or semi-refined naphthenic acids which process, in its simplest aspect, relates to the treatment of naphthenic acids with oxygen-containing inorganic acids of such concentration that the formation of emulsions is substantially prevented and a ready separation of the sludge formed upon acid treatment may be realized. For instance, sulphuric acid, having a concentration between approximately 50% and 83% has been found especially suitable. While any oxygen-containing inorganic acid such as iodic acid, chloric acid or bromic acid has been disclosed as suitable for the separation of the carbonaceous materials, I preferably use an oxygen-containing inorganic acid chosen from the class comprising sulphuric, phosphoric or nitric acid. The amounts of these acids to be used are relatively small and range from to volume percent of the naphthenic acids.

If desired, the acid treatment referred to above,

may be carried out in the presence of a hydrocarbon diluent such as liquid propane, butane, cleaners naphtha (a petroleum fraction boiling between ZOO-300 F.) benzol or the like. The addition of any of the above mentioned diluents greatly facilitates the separation of the sludge formed as a result of the acid treatment.

I have discovered in connection with the present invention that a similar facilitation of the sludge settling may be brought about by increasing the temperature of the acid treat to temperatures ranging from approximately 100 to 200 F.

While in the above identified application it is indicated that the strength of the acid used for the removal of the carbonaceous materials should preferably be between 50% and 83%, I

have found that acids of greater concentration I may be used as well and that such acids are especially effective when a naphthenic acid product of light color is desired. As such concentrated acids are more or less miscible with the naphthenic acids, steps must be taken to provide for the removal of these acids as well as for the acid sludge. Thus 95% sulphuric acid, fuming sulphuric acid (containing about 15% dissolved S03) as well as sulphuric acid having a concentration of between 83% and 95%, tend to be substantially miscible with the naphthenic acids.

When the impure naphthenic acids containing carbonaceous materials are contacted with to 10 volume percent of sulphuric acid having a concentration substantially that set out above, no separation into phases takes place, although in some cases the carbonaceous materials agglomerate. However, when portions of more dilute sulphuric acid (e. g. sulphuric acid of 60% concentration) are added to the mixture of impure naphthenic acids and the highly concentrated sulphuric acid, a separation into a naphthenic acid phase and a phase consisting of sludge, sulphuric acid and carbonaceous materials readily takes place as soon as the total acid concentration has been reduced to approximately 83%. The carbonaceous materials are found in the sludge and sulphuric acid layer.

Another method of obtaining phase separation when such concentrated acids are being used to obtain a higher degree of decolorization and deodorization consists in diluting the naphthenic acids either before or after treatment with the concentrated sulphuric acid, with a material capable of reducing the solvent power of the sulphuric acid for the naphthenic acid. Liquid propane, cleaners naphtha, petroleum ether or other light parafiinic solvents may be used for this purpose. Aromatic hydrocarbons such as benzol, toluol or their homologues may be used for the purpose indicated above but are not as desirable as the parafiinic solvents on account of their solubility in the concentrated sulphuric acid. The above mentioned diluents may be removed from the naphthenic acids by distillation or by extracting the mixture of naphthenic acids and diluent with an alkaline material, such as caustic soda and liberating the naphthenic acids from their salts so produced by means of an inorganic acid, such as E804, HCl or the like.

The so treated acids are then treated with the adsorbent material in the manner described herein, to further improve their color and odor.

When the crude or semi-refined naphthenic temperatures substantially in excess of atmospheric, no improvement in the color thereof could be noted.

When, however, the carbonaceous materials are removed from the naphthenic acids by means of any of the oxygen-containing inorganic acids set forth in the above identified copending application or by any other means and the so treated acids are subjected to a treatment with an adsorbent material a Vast improvement in the color and odor of the final product as compared with the crude or semi-refined acids is brought about.

For example, in a preliminary experiment, im-

pure naphthenic acids which had been treated with 0.5% by volume of 80% sulphuric acid for purposes of removing the carbonaceous materials admixed therewith, and which had a color in excess of 8 N. P. A., were contacted with 10% of fullers earth for minutes at a temperature of- 300 F. After filtering off the adsorbent and the materials taken up thereby, naphthenic acids having a color of from 4% to 5 N. P. A. was obtained. The same acids, Without preliminary acid treatment, when contacted with the same adsorbent under identical conditions showed no improvement in color whatsoever.

Considering my process in greater detail, a charge of crude or semi-refined naphthenic acids contaminated with carbonaceous materials and having a dark red to black color, is treated with an oxygen-containing inorganic acid such as sulphuric acid. The amount of acid used may vary between /2 to volume percent of the, naphthenic acids. The concentration thereof is chosen preferably between 50% and 83%. The mixture of inorganic acid and naphthenic acids is agitated with air or by mechanical means preferably for a period of from to 30 minutes. Just before the agitation is stopped, a small amount of clay or water is added to facilitate the separation of the acid sludge. The sludge is subsequently separated together with the carbonaceous materials. The naphthenic acids are then washed with water to remove any inorganic acidity and are then blown at a slightly elevated temperature with natural gas or any inert hydrocarbon gas to remove the remaining traces of water.

The naphthenic acids, treated as indicated above, have a much improved color but are still too dark for a commercial product. These acids are now mixed at ordinary temperatures or at least at temperatures below the boiling point of water, with the adsorbent, the amount of the latter being somewhere between approximately 8 and depending upon the particular charge of the naphthenic acids and the degree of decolorization desired. The mixture of naphthenic acids and adsorbent is heated while agitating with air or by other means, such as a mechanical stirrer up to a temperature ranging from approximately 225F. to 300 F. or higher. As soon' as the desired temperature hasbeen reached, which in most instances is somewhere between 250 F. and 325 F., the heating is discontinued or slowed down and the mixture is maintained at this temperature for a period of approximately 2 to 5 minutes. The agitation is then discontinued, and the purified and decolorized naphthenic acids are separated from the adsorbent by filtering them while still in a heated condition through a suitable filtering device such as a Sweetland filter. It is not essential that the filtering process takes place at an elevated temperature. However, the viscosity of the naphthenic acids at an elevated temperature is such to allow a more rapid filtration. The naphthenic acids so obtained have a color of from 4 to 6 N. P. A. as compared with a color in excess of 8 N. P. A. before treatment with the adsorbent.

As a slight modification of the above operation, it may be desirable in connection with the purification of the naphthenic acids to eliminate the water wash of the naphthenic acids for re moval of the inorganic acidity and thus leave a small amount of sulphuric acid or any equivalent acid, admixed with the naphthenic acids. When the naphthenic acids containing a small amount of inorganic acidity are treated with the adsorbent material a product is obtained which has a lighter color than one which had been waterwashed before treatment with the adsorbent. It is believed that the presence of the inorganic acidtends to activate the adsorbent material.

if for, any reason a water wash of the naphthenic acids should be deemed desirable, the ad-' sorbent may be activated by addition of small amounts of an inorganic acid such as that used for the removal of the carbonaceous materials or these acids may be directly added to the naphthenic acids before treatment with the adsorbent as pointed out above. Acid salts such as sodium acid sulphate, sodium acid phosphate or the like may be substituted for the inorganic acids and produce almost identical results. It has been found advantageous, especially in the case where the residual inorganic acid is used for activating the adsorbent material, to introduce a small amount of water with the adsorbent, or adding the adsorbent in the form of a water containing slurry. The presence of the water appears to causea better dispersion of the inorganic acid and hence abetter activation of the adsorbent material.

The amount of the adsorbent to be used will vary with the naphthenic acid stock to be treated,

the degreeof decolorization and the particular adsorbent used. In general, amounts of from 8 to 20% of the adsorbent material as indicated above are sufficient, although in certain instances where a light colored product is desired, from 40% to 51% of the adsorbent material may be required. "yThe treating temperature with the adsorbent material referred to above has been indicated to be somewhere between approximately 225 F. to F. However, very successful treatments have been made at temperatures of 400 F. or above. The above temperature range is merely my preferred operating temperature. Naphthenic acids, freed from carbonaceous materials by any of the processes set forth herein, show an improvement in color even when treated at room temperature. The upper treating temperature limit is largely controlled by the boiling point and flash point of the naphthenic acids. a

The time interval during which the naphthenic acids are contacted with'the adsorbent material may vary .over a wide range. In general, 2 to 15 minutes are sufiicient to bring about the desired decolorization although contact times considerably in excess of these may be necessary in certain instances.

The following specific examples are illustrative of my invention:

Example 1 Fifteen hundred (1500) cubic centimeters of semi-refined naphthenic acids containing from 3% to 5% of carbonaceous materials were agitated with 75 cubic centimeters of sulphuric acid for one-half hour. Immediately before the agitation was stopped, 5 grams of diatomaceous earth were added to the mixture to facilitate the The finished product in each instance had an acid number of from 289-290 as compared with an acid number of 284 before treatment.

The following example is illustrative of the improved decolorizing action of the adsorbent when small amounts of sulphuric acid are left in the naphthenic acids which in this case is accomplished by eliminating the water wash. The stock used consisted of semi-refined naphthenic acids which had been agitated with 5 volume percent of 80% H2804. (About 1% of clay was added to facilitate the settling of the sludge.) The results of the treatment of these acids with the adsorbent in comparison with naphthenic acids which had been water washed for removal of the sludge are given below:

Table II Semi-refined naphthenic Type of acids acid treated Same Same Same as indicated above Water wash None None Agitated w' h 10% E10. Same. Clay usedamount 10%Filtrol. 10% Filtrol- 10% Filtrol- 10% Filtrol. Clay treating temperature 200 F 225 F 225 F 225 F. Duration of clay treating 2 min 2 min 2 min 2 min. Color of filtrate 4% N. P. A 4% N. P. A. 6% N. P. A 6% N. P. A.

settling of the sludge. The naphthenic acids, now substantially free from the above mentioned carbonaceous materials, were washed with hot salt water and after removal of the wash water, were blown bright with natural gas, at a temperature of about 180 F. They were transparent when viewed through the neck of a four ounce oil sample bottle, whereas the untreated acids were black and had no such transparency.

The naphthenic acids which had been purified as indicated above were then mixed at room temperature with approximately 10% by weight of Filtrol. Individual samples of the mixture were slowly heated up to a temperature of approximately 212 F. to cause a dehydration of the adsorbent in such a manner that no undue foaming of the mass occurred and they were then heated to various temperatures ranging from 225 F. to 300 F. The naphthenic acid charges, during heating, were agitated by means of a slow current of air. When the desired temperature had been reached, the heating of the charges was slowed down or discontinued and the mixture of naphthenic acid and clay was allowed to remain at this temperature for approximately two minutes. The acids were then removed from the adsorbent materials by passing the mixture through a suitable filtering device. This filtration was carried out at substantially the same elevated temperature which prevailed during the clay treatment which greatly facilitated the rate of filtration.

The finished product had a permanent color of from 4% to 5% N. P. A. and was of a bland to sweet odor as may be seen from the following table:

Table I In case an extremely light colored product such as one having a color of between 2 /2 and 3 N. P. A. is desired, the treatment with the adsorbent material, or with an adsorbent material which has been activated by means of sulphuric acid, phosphoric acid or the like, or by means of an acid salt as indicated above, may be repeated. Thus, a product having a color of 3%; N. P. A. was obtained by treating naphthenic acids which had been purified as indicated above and which had a color of 4% N. P. A. with 10% of Filtrol which had been activated by means of 0.33% of 60% sulphuric acid, at a temperature of 325 F. A small amount of water (10% by volume of the naphthenic acids) was added to the adsorbent before introduction into the naphthenic acids. The time of contact with the adsorbent material was approximately 15 minutes.

While the removal of the carbonaceous material from the naphthenic acids has been disclosed to be performed by means of distillation, or preferably by treatment with an oxygen-contaim'ng inorganic acid, such as sulphuric acid or the like, other means may be employed for the same purpose. Thus, carbonaceous materials may be readily removed from naphthenic acids which are present by means of sulphur trioxide dissolved in cleaners naphtha or kerosene, or by means of concentrated aqueous solution of ferric chloride or zinc chloride in amounts substantially the same as used in the case of the inorganic acids described above, or by passing dry hydrogen chloride or other hydrogen halides into the naphthenic acids containing the carbonaceous materials, or by treating the impure naph- Stock treated Semi-refined acid Semi-refined acid Semi-refined acid Semi-refined acid Vol. of acid treat Adsorbent used 5 vol. percent of 5 vol. percent of 2804- Filtrol 5 vol. percent of 5vol. percent of80% Filtrol. 300 F. 2 min. lack. 4% N. P A

thenic acids with concentrated aqueous solutions of hydrogen halides. The function of any of the above reagents is to coagulate the carbonaceous materials to particles large enough to settle under the influence of gravity. I have discovered that naphthenic-acids which have been freed from carbonaceous material by means of any of the above mentioned reagents are readily amenable to treatment with an adsorbent material in the manner described above.

While the process of deodorization and decolorization has been particularly described in connection with phenol-free or semi-refined naphthenic acids, it may equally well be applied to naphthenic acids which have not been subjected to a process for the removal of phenolic materials such as that previously described. However, such products do not possess as desirable a color and odor as the naphthenic acids which had been freed from phenolic material.

The term blowing bright referred to earlier in this specification, relates to the treatment of naphthenic acids or other hydrocarbon products with an inert gas, such as air or methane, ethane, and the like, for removing traces of water which remain in the naphthenic acids or other liquid hydrocarbon after a treatment thereof with Water or aqueous solutions.

The term Filtrol signifies an acid treated clay or fullers earth. The product commercially marketed under that name consists of fullers earth which has been activated by means of dilute sulphuric acid.

The term N. P. A. color used in this specification relates to a color grade of a liquid obtained by means of the Union Petroleum Colorimeter adapted as a standard of the National Petroleum Association in 1915. A detailed description of the apparatus, method of test and significance of scale readings may be found in David T. Day's Handbook of Petroleum Ind., 1922, vol. 1, page 656. For example N. P. A. 0.51 indicates a light, almost water-white color, wherein N. P. A. 3 indicates a yellow. to straw color and N. P. A. '7 to 8 indicates a product of a dark reddish to brown color.

The process herein set forth is applicable to all varieties of naphthenic acids. It may be equally well applied to naphthenic acids derived from a light petroleum fraction such as kerosene as to acids derived from the higher boiling fractions such as gas oil or lubricating oil.

The examples set forth herein are merely illustrative of the generic invention and many variations thereof will be obvious to those skilled in the art.

I claim:

1. A method of purifying naphthenic acids which comprises treating said acids at an elevated temperature ranging from approximately 100 to 200 F. with sulfuric acid of a strength capable of agglomerating carbonaceous impurities.

2. A method asclaimed in claim 1 in which the treatment is carried out in the presence of a water immiscible diluent.

3. A method of treating naphthenic acids which comprises diluting said acids with a water immiscible solvent which has a boiling point range different from that of the naphthenic acid, treating the diluted naphthenic acid with .5 to 10% by volume of concentrated sulphuric acid, and then recovering the treated naphthenic acids dissolved in the water immiscible solvent.

4. A method'as claimed in claim 3 in which the sulphuric acid is about 95.0% in strength.

5. A method as claimed in claim 3 in which the solvent is petroleum naphtha.

6. The process of purifying crude naphthenic acids which comprises diluting the acids with a water-immiscible solvent which has a distillation boiling point range different from that of the crude acid, treating the diluted crude acids with a strong sulfuric acid and recovering the treated naphthenic acids dissolved in the waterimmiscible solvent. 1

'7. The process of purifying crude naphthenic acids which comprises diluting the acids with a water-immiscible solvent of lower distillation boiling point range than that of the crude acids, treating the diluted acids with a strong sulfuric acid and recovering the treated naphthenic acids dissolved in the water-immiscible solvent.

8. A method as claimed in claim 6 in which the water-immiscible solvent is a hydrocarbon.

9. A method as claimed in claim 6 in which the water-immiscible solvent is a petroleum naphtha.

10. A method of treating naphthenic acids which comprises diluting said acids with a waterimmiscible solvent which has a boiling point range different from that of the naphthenic acids, and treating the diluted naphthenic acids with .5 to 10% by volume of concentrated sulfuric acid.

11. A process for purifying naphthenic acids containing admixed carbonaceous materials and color bodies, the steps of diluting the said naphthenic acids with a low boiling hydrocarbon fraction, contacting the diluted acids with sulfuric acid having a strength of between 50 and 83%, separating the agglomerated materials and acid sludge, and separating the hydrocarbon diluent from the naphthenic acids.

FREDERICK J. EWING. 

